1. Field of the Invention
The present invention relates generally to a head up display device, and more particularly to a head up display device that is suitable to be disposed in a vehicle.
2. Description of Related Art
Conventionally, as an example of a head up display device (hereinafter referred to as an HUD device), there is an HUD device for a vehicle described in JP-A-H08-002287. The HUD device for the vehicle displays a virtual image at a desired position for a user'(driver). The HUD device for the vehicle includes a display unit having a display that displays an image, and a reflective member that reflects the image displayed on the display to project the image onto a projection member provided for the vehicle, such as a windshield. The image projected on the windshield from the display unit is displayed as a virtual image.
This HUD device includes a stepping motor that changes a projection position of the image on the windshield by rotating the reflective member to change a display position of the virtual image. This stepping motor is rotated through the operation of an operating switch by the driver. Accordingly, the virtual image can be displayed at the driver's favorite position.
The stepping motor used for the HUD device rotates a magnet rotor by the application of a drive signal whose amplitude periodically changes to a coil. This application of the drive signal is carried out in accordance with a step signal outputted from an oscillator. The oscillator outputs a step signal when a forward signal or reverse signal from the operating switch is inputted thereinto.
Generally, in a stepping motor that employs a magnet rotor for a rotor, it is noted that the magnet rotor is held at a stabilizing point at which detent torque becomes the greatest. By maintaining a rotation angle of the magnet rotor using the detent torque as above, waste of consumed electric power of the stepping motor can be curbed as much as possible.
However, if a size of a stator for fixing the coil of the stepping motor, or a magnetizing position of a magnetic pole of the magnet rotor varies, an actual stabilizing point of the magnet rotor and a quiescent point of the magnet rotor at the time of application of the drive signal to the coil become different. Accordingly, if the application of the drive signal to the coil is stopped to limit the waste of the consumed electric power of the motor, the magnet rotor rotates by a minute angle, and the virtual image thereby vibrates.
When changing the display position of the virtual image, the user (driver) raises awareness of a display state of the virtual image, and is sensitive to a slight movement of the virtual image. Accordingly, if the virtual image vibrates immediately after the completion of rotation of the reflective member, i.e., while the user's awareness of the display state of the virtual image is being heightened, a sense of discomfort may be brought to the user.